Skipping responses

I've came across a very specific scenario where due to a high volume of write requests, calling `tcpsock:receive` after every operation was too expensive. In this scenario, counters on Redis were incremented and decremented in a *write-and-forget* fashion.

For this reason I've introduced a new `skip_responses(bool_skip)` function to be able to optionally instruct the client to discard every response by skipping the `tcpsock:receive` function call.

I've submitted this pull request just in case somebody else needs it.